1. Field of the Invention
The present invention relates to a refrigerator having a compressor and a control unit for selectively activating and deactivating the compressor in response to predetermined cut-on and cut-off temperatures inside the refrigerator.
2. Description of the Related Art
It is generally recognized in the domestic refrigeration technical field that a user through a user interface (e.g. knobs) can vary the cut-off and cut-on temperature values. When the user wants to select a lower food conservation temperature, the interface can be adjusted accordingly. The control unit detects the change and varies the cut-off temperature accordingly. The cut-on temperature can vary too (therefore maintaining the same interval between cut-off and cut-on temperatures) or can be kept constant (particularly in fridge compartment). In the fridge compartment the activation of the compressor can be conditional upon detection of a proper temperature on the evaporator (for avoiding frost build-up).
In addition to the “manual” setting of the desired degree of refrigeration in the food conservation cavity (or in the electronic models in addition to the setting of the average temperature of the cavity), the control unit senses the actual temperature of the cavity and, if it is equal or above the cut-on temperature, activates the compressor or, if it is equal or below the cut-off temperature, deactivates the compressor. The temperature inside the cavity is therefore oscillating between the cut-on and cut-off temperature.
It is also generally recognized that the storage temperature inside the refrigerator cavities (either fridge or freezer) should be kept as constant as possible for the whole period of storage. For some food products even a small variation has serious consequences. For example, fluctuations of temperature often cause condensation of moisture on stored products, which is undesirable because it may favor the growth of microorganisms. In tests carried out by the applicant, one of the main causes of fluctuations of temperature is a “special event” such as the addition of a big load in the storage cavity, a door opening longer than usual or a black out. Following a special event, even if the temperature of air in the cavity goes back quite shortly to the nominal value, the temperature of food takes a longer time for returning to the same value before a special event. Since the recovery of food temperature is more important, in term of food conservation, than the recovery of air temperature in the cavity, it became clear to the applicant that the known control systems could not cope with the temperature oscillation of the food stored in the cavity. Accordingly, it would be advantageous to provide a refrigerator that maintains a lower fluctuation of the temperature of the stored food in the cavity.